- Configure all subdomains to point to the same server IP as the main domain
- Configure all subdomains in virtual host to point to the same location as the main domain
What is the easiest way to do this?
Go into your DNS settings and simply setup a new A record for the sub domains, and set the target to the same one as the main domain.
The DNS settings you're looking for are going to be with the company where you registered the domain. If you did it through Nexcess, speak to them about setting it up. If you got the main domain through another registrar (e.g. GoDaddy, NetworkSolutions, Hover, etc.) then you'll go through that registrar's tools to setup the DNS.
Each domain registrar has they own slightly different way to configure DNS.